Cardiac resynchronization therapy (CRT) is a treatment for heart failure patients in which one or more heart chambers are electrically stimulated (paced) to restore or improve heart chamber synchrony. Improved heart chamber synchrony is expected to improve hemodynamic performance of the heart, such as assessed by ventricular pressure and the rate of change in ventricular pressure or other hemodynamic parameters, thereby alleviating symptoms of heart failure. Achieving a positive clinical benefit from CRT is dependent on several therapy control parameters, such as the atrio-ventricular (AV) delay, inter-ventricular (VV) delay and pacing site(s). The AV delay controls the timing of ventricular pacing pulses relative to an atrial depolarization, intrinsic or paced. The VV delay controls the timing of a pacing pulse in one ventricle relative to a paced or intrinsic sensed event in the other ventricle. Pacing may be delivered in the right ventricle and/or the left ventricle to restore ventricular synchrony.
Atrial conduction disorders are common in heart failure. When atrial-ventricular timing is not optimal, the atrial contribution to ventricular filling can be diminished, which can reduce ventricular ejection and hemodynamic performance. Implantable devices and associated methods are needed for delivering CRT in a manner that reduces risks of atrial conduction disorders.